With PLOTYY you can add a new axis, which will be linearly related with the old one. With this function, the new axis may be related by ANY monotonic ascending or descending function with the old one (which should be specified), and works with the x-axis as well.

Besides, both axes will be linked to work with the ZOOM/PAN functionalities and even the DATETICK or TLABEL function for a time axis.

For example, to include a new x-axis with an exponential relationship with the old one just use:
>> addaxes('XFun','exp')